Catechols are defined as members of a family of aromatic diols having a substituted 1,2-benzenediol skeleton. Tiron, also known as 1,2-dihydroxybenzene-3,5-disulfonic acid, is one member of the catechol family and has the molecular structure shown in Scheme 1. Other sulphonated catechols also exist. In addition to the disulfonic acid, the term “Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid)” may also include mono- or di-sulfonate salts of the acid, such as, for example, the disodium sulfonate salt.

Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid) and other catechols bind to ions of certain transition metals, such as ions of iron and titanium, and form colored metal/chelant complex. For example, in solutions Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid)binds to ferric iron (Fe3+) to form a burgundy red metal/Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid) complex. The presence of this colored Fe3+/Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid) species may be detected at metal ion concentrations of 0.1 parts per million (ppm) or even lower. Thus, Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid) has traditionally been used as a colorimetric indicator/chelant for the presence of titanium or iron.
Catechols, such as Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid), are also small molecule chelants that may be used as cleaning agents. For example, Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid) delivers robust hydrophilic cleaning benefits and may also drive particulate cleaning via clay peptization, suspension, and/or synergy with polymeric dispersing systems. In addition, Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid) may be compatible with certain enzymatic cleaning agents used in certain detergent compositions.
However, many detergent compositions contain low concentrations of soluble iron, such as ferric iron. The concentration of ferric iron in these detergents is enough to form sufficient metal/chelant complexes with certain catechols, such as Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid), to give the detergent an undesirable reddish color. This is particularly true for liquid detergent compositions in which the soluble ferric iron may freely complex with the Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid) in the liquid detergent. For example, addition of low levels of Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid) to commercially available detergents results in the detergent acquiring a reddish hue associated with the formation of the iron/Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid) complex.
Many consumers may disfavor reddish colored detergents. For example, a reddish color in detergent may be associated with rust. Thus, in order to produce detergent compositions within the blue color space, many detergent producers specifically avoid red chromophores. The presence of red chromophores in a detergent formulation may result in additional cost required to remove the red color from the detergent. Since detergents comprising certain catechols, such as Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid), would result in a reddish hue to the detergent composition due to the presence of ferric iron, many catechols, including Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid), have not traditionally been used in detergent applications, particularly in liquid detergents.
It would be desirable to produce a detergent possessing the cleaning benefits associated with Tiron (1,2-dihydroxybenzye-3,5-disulfonic acid) without the concomitant formation of the reddish iron/chelate complex.